Distributor fuel injection radial piston pump

ABSTRACT

A distributor fuel injection radial piston pump comprising a distributor piston movable between first and second axial positions to communicate a pump working space with an injection nozzle and to prevent communication between the pump working space with the injection nozzle, a control valve for controlling a quantity of fuel fed to the injection nozzle and movable between open and closed position to communicate the pump working space with the pump interior therethrough in the open position thereof to prevent feeding of fuel to the injection nozzle and blocking communication between the pump working space and the pump interior therethrough in the closing position thereof to provide for feeding fuel to the injection nozzle, and means for preventing excessive feeding of fuel to the nozzle in case of failure of the first control valve to move from the closing position thereof to the open position thereof in response to a predetermined control signal, the preventing means including a control space defined at least partially by the end face of the distributor piston and a second control valve for changing pressure in the control space to move said distributor piston to the second axial position thereof in which feeding of fuel to the injection nozzle is prevented.

BACKGROUND OF THE INVENTION

The invention relates a distributor fuel injection radial piston pumpfor internal combustion engine.

In such distributor fuel injection pumps, such as are described, forexample, in the German Patent Application No. P 36 12 942.9, the pumpwork space is always completely filled with fuel during the suctionstroke of the pump piston. The quantity of the injected fuel volume isdetermined as a function of parameters of the internal combustionengine, such as load and speed, by a point of time at which the electriccontrol valve is closed and opened. When the control valve closes, thefuel is injected into the respective cylinder of the internal combustionengine, whereas the pump work space communicates with the relief spacewhen the control valve opens and the fuel injection is accordinglycorruptly terminated. When there is a defect in the control valve suchthat it remains stuck in its closing position and no longer opens, theinternal combustion engine is always supplied with a maximum fuelinjection quantity regardless of load, and the speed of the internalcombustion engine accumulates in such a way that it cannot be influencedand the internal combustion engine "races".

SUMMARY OF THE INVENTION

The object of the invention is a distributor fuel injection pump, inwhich delivery of fuel from the pump work space to an injection nozzleis interrupted in the event the control valve becomes stuck in itsclosing position. The internal combustion engine accordingly stops dueto the absence of an ignition mixture. The defect in the control valveis detected by a monitoring device which then transmits a closingcommand to the second control valve. The increase in speed of theinternal combustion engine over a maximum speed, for example, can be acriterion for the defect in the first control valve. The second controlvalve is preferably constructed in such a way that it is normally closedand opens when controlled. The second control valve closes when thecontrol stops. The closing command consists in an interruption of theexciting current for the electromagnet of the second control valve. Inthis way, the fuel delivery is also interrupted when the control line ofthe second control valve experiences disturbance. The second controlvalve can be much simpler and accordingly cheaper than the first controlvalve.

DRAWING

The invention as to its construction so as to its method of operation,together with additional objects and advantages thereof, will be bestunderstood from the following description with reference to theaccompanying drawing, wherein

FIG. 1a shows a longitudinal cross-sectional view of a first embodimentof a distributor fuel injection radial piston pump according to thepresent invention in a normal operating position thereof;

FIG. 1b shows a longitudinal cross-sectional view of the pump shown inFIG. 1a but in a position when its normal operation is interfered with;

FIG. 2a shows a longitudinal cross-sectional view of a second embodimentof a distributor fuel injection radial piston pump according to thepresent invention in a normal operating position thereof;

FIG. 2b shows a longitudinal cross-sectional view of the pump shown inFIG. 2a but in a position when its normal operation is interfered with;

FIG. 3a shows a longitudinal cross-sectional view of a third embodimentof a distributor fuel injection radial piston pump according to thepresent invention in a normal operating position thereof;

FIG. 3b shows a longitudinal cross-sectional view of the pump shown inthe FIG. 3a but in a position when its normal operation is interferedwith;

FIG. 4a shows a longitudinal cross-sectional view of a fourth embodimentof a distributor fuel injection radial piston pump according to thepresent invention in a normal operating position thereof;

FIG. 4b shows a longitudinal cross-sectional view of the pump shown inFIG. 4a but in a position when its normal operation is interfered with.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A distributor fuel injection radial piston pump shown in FIG. 1comprises a cup-shaped housing 10 and a cover 11 closing the latter,which cover 11 is slid in from the open end of the housing 10 anddefines a pump interior 12 with a base 10a which forms one piece withthe housing 10. The pump interior 12 is filled with fuel under lowpressure and is connected with a fuel return line leading to a fuel tank(neither one is shown) via an outlet opening 13 with a throttle 14located upstream thereof. A drive shaft 15 extends through the base 10ahousing 10 and is to sealed against fluid leakage. The shaft 15 widensin a cup-shaped manner in the pump interior 12 and carries a cam ring 16along its edge, which cam ring 16 is connected thereto for jointrotation therewith fixed. On its inside, the cam ring 16 has a cam face17 with radially inwardly directed cams which correspond in number andsequence to the number and sequence of radial pump pistons of the fuelinjection pump, and to the number of piston strokes of these pumppistons per a revolution of the drive shaft 15. A feeding pump 18 issupported on the drive shaft 15 and is connected with the fuel tank viaan inlet line 19 and with the pump interior 12 via a pressure line 20and accordingly ensures the filling of the pump interior 12 with fuel.

In addition, a distributor piston 21 is connected to the drive shaft 15for joint rotation therewith but for axial displacement relativethereto. The axis of the distributor piston is aligned with the axis ofthe drive shaft 15. The distributor piston 21 is guided in a distributorcylinder 22 until the end which is connected with the drive shaft 15 inthe pump interior 12. The distributor cylinder is held in a bore 23 ofthe cover 11, which bore 23 is coaxial with the axis of the drive shaft15. Guides 24, which are uniformly distributed along the circumferenceof the distributor cylinder 22 and extend until the vicinity of thedistributor piston 21, are provided in the cover 11 and in thedistributor cylinder 22 adjacent to the cam face 17 so as to beconnected in a radially inward direction. For a distributor injectionpump shown in FIG. 1 for supplying a total of three injection nozzles ofan internal combustion engine, particularly a diesel engine, there is atotal of three guides 24, only one of which can be seen in FIG. 1.Radial through holes 25 are provided in the distributor cylinder 22coaxially relative to the guides 24. A pump piston 26 is guided into theradial through holes 25 in each instance so as to be longitudinallydisplaceable. A so-called roller tapper 27, which comprises a roll orroller 28 and a tappet cup 29, is guided into the guides 24 in eachinstance so as to be longitudinally displaceable. A tappet spring 31,which is supported on the base of the guide 24, on one side, and at aspring disk 30 contacting the base of the tappet cup 29 on the otherside, presses the tappet cup 29 against the roller 28 and the latteragainst the guide face 17. The spring disk 30 engages behind a collar26a of the pump piston 26, which collar 26a projects out of the radialthrough bore-hole 25, and accordingly fastens the collar 26a at thetappet cup 29.

Every pump piston 26 defines a pump work space 32 in the radial throughhole 25, the pump work space 32 being defined, on the other hand by anannular groove 33 on the distributor piston 21. A distributor groove 34and a filling groove 35 open into the annular groove 33 and extend awayfrom the annular groove 33 axially in opposite directions on thedistributor piston 21. Three injection bores 36, which are uniformlydistributed along the circumference of the distributor cylinder 22 andlead through the distributor cylinder 22 and the cover 11 until aninjection nozzle 37, open into the interior of the distributor cylinder22 in a cross-sectional plane. One of the three injection nozzles 37 isshown schematically in FIG. 1. The axial length of the distributorgroove 34 is dimensioned in such a way that it projects until thecross-sectional plane of the openings of the injection bores 36 andaccordingly connects one of the three injection bores 36 with theannular groove 33 according to the rotational position of thedistributor piston 21. In another cross-sectional plane in the vicinityof the end of the distributor cylinder 22 facing the pump interior 12,three filling bores 38 open into the interior of the distributorcylinder 22 and are arranged so as to be uniformly distributed at thecircumference of the distributor cylinder 22. The axial length of thefilling groove 35 is dimensioned in such a way that it projects untilthese cross-sectional planes of the openings of the filling bores 38 andaccordingly, connect one of the three filling bores 38 with the annulargroove 33 according to a rotational position of the distributor piston21. The coupling of the distributor piston 21 to the drive shaft 15 iseffected via a pin-in-slot connection in which a driving pin 39 engagesat the drive shaft 15 in a form-locking manner in a longitudinal groove40 in the distributor piston 21. The basic position of the distributorpiston 21 shown in FIG. 1 is fixed by a helical pressure spring 41 whichbiases the end of the longitudinal groove 40 against the driving pin 39which, accordingly, forms a limiting stop for the axial displacingmovement of the distributor piston 21.

The valve housing 42 of an electric control valve 43 is placed on theoutwardly facing front side of the cover 11 and is fastened there in acorresponding manner. The valve housing 42 engages with a centering pinin the inner hollow space of the distributor cylinder 22 and defines acontrol space 44 together with an end face 71 of the distributor piston21 opposite it. The construction of the control valve is known and isdescribed, e.g. in the DE-OS No. 35 23 536. Briefly stated, the twovalve connections 45, 46 of the control valve 43 are connected with oneanother via a valve opening 47 which is controlled by an electromagnet.A valve member 48 is actuated by an electromagnet 49, wherein the valvemember 48 releases the valve opening 47 in the unexcited state of theelectromagnet 49 by the action of a return spring, not shown, and closesit in the excited state of the electromagnet 49. The valve connection 45overlaps a first bore portion 51 of a relief line 50 opening into thefront side of the cover, whereas the second valve connection 46 overlapswith an opening of a second bore portion 52 of the relief line 50, whichopening is located in the front side of the cover 11. The pump workspace 32 communicates with the pump interior 12 via the relief line 50.

The pressure line 20 between the feeding pump 18 and the pump interior12 extends in the distributor cylinder 22 via the control space 44, thepressure line 20 being divided into first and second line portions 53,54 by the distributor cylinder 22. A second electric control valve 55,controls a valve opening 57 in the second line portion 54 with a valvemember 56 arranged in the second line portion 54 which connects thecontrol space 44 with the pump interior 12. The valve member 56 isactuated by an electromagnet 58. The valve member 56 closes the valveopening 57 in the unexcited state of the electromagnet 58 due to theaction of a valve closing spring 59 and opens it in the excited state ofthe electromagnet 58. The second control valve 55 is controlled by amonitoring device 60 which continuously monitors the unobjectionablefunctioning of the first control valve 43 and transmits a closingcommand to the second control valve 55 by turning off the excitingcurrent for the electromagnet 58 as soon as the valve member 48 of thefirst control valve 43 does not open in spite of the absence of theexcitation of the electromagnet 49. Such a monitoring device 60 can beformed, e.g., as a speed detector which transmits the closing command tothe second control valve 55 when the speed of the internal combustionengine exceeds a predetermined maximum speed, which is an indicationthat the first control valve 43 no longer opens. When the second controlvalve 55 closes, the connection of the control space 44 to the pumpinterior 12 is blocked and a pressure is built up in the control space44 by the feeding pump 18, which pressure moves the distributor piston21 to an axial displacing position shown in FIG. 1b. In this axialdisplacing position, an opening of a hole 61 which is otherwise closed,is opened by the distributor piston 21, and it now connects the controlspace 44 with the pump interior 12. In addition, as shown in FIG. 1b,the end of the distributor piston 21 facing the pump interior 12 ispushed out of the distributor cylinder 22 far enough so that the fillinggroove 35 is open toward the pump interior 12 and forms a continuousconnection between the pump work space 32 and the pump interior 12.

The manner of operation of the fuel injection pump described above is asfollows:

During a suction stroke of the pump piston 26, the latter moves radiallyoutward as a result of the sliding of the roller tappet 27 on adescending flank of the cam face 17. The rotational position of thedistributor piston 21 is such that the filling groove 35 overlaps thefilling bore 38. The first control valve 43 is open in an absence ofcurrent and the second control valve 55 is likewise opened by appliedcurrent. Fuel now flows into the pump work space 32 via the filling bore38, the filling groove 35 and the annular groove 33. After the pumppiston 26 passes through the bottom dead center position, the dischargestroke of the pump piston 26 begins, wherein the pump piston 26 movesradially inward as a result of the sliding of the roller tappet 27 on anascending flank of the cam face 17. In so doing, fuel is guided backinto the pump interior 12 from the pump work space 32 via the reliefline 50 and the first control valve 43 which is still open. At apredetermined point of time during the discharge stroke, the firstcontrol valve 43 is closed during the delivery stroke. The distributorpiston 21 has then, at the latest, reached a rotational position inwhich the distributor groove 34 overlaps the injection bore 36 and,accordingly, connects the pump work space 32 with the assigned injectionnozzle 37 via the injection bore 36. Fuel is now fed to the injectionnozzle 37 from the pump work space 32 and is injected into the cylinderof the internal combustion engine. In order to terminate the fuelinjection, the first control valve 43 is switched to the currentlessstate so that, upon opening control valve 43 connects the pump workspace 32 to the pump interior 12 via the annular groove 33 and therelief line 50. The pressure in the pump work space 32 suddenly dropsbelow the opening pressure of the injection nozzle 37 and closes it. Thefuel quantity which is delivered to the injection nozzle 37 and injectedtherefrom is metered in accordance with the time of closing and/oropening of the first control valve 43.

FIG. 1b shows the fuel injection pump in the event when the firstcontrol valve 43 is defective, and its valve member 48 does not open thevalve opening 47 in spite of the absence of the exciting current for theelectromagnet 49. This is a case of the first control valve 43 stickingin the closing state. Because of this defect, the entire quantity offuel contained in the pump work space 32 is injected via the injectionnozzle 37 during every discharge stroke of the pump piston 26. The speedof the internal combustion engine accordingly constantly increases. Thisexcessive speed of the internal combustion engine is detected by themonitoring device 60 and the latter transmits a closing command to thesecond control valve 55. This closing command turns off the excitingcurrent for the electromagnet 58 of the second control valve 55. Thesecond control valve 55 closes due to the action of the valve closingspring 59. Accordingly, the control space 44 in the distributor cylinder22 is separated from the pump interior 12. As a result of fuel supply bythe feeding pump 18, the pressure in the control space 44 increases anddisplaces the distributor piston 21 into the axial displacement positionshown in FIG. 1b. In this displacement position, the filling groove 35,which opens into the pump work space 32, extends into the pump workspace 12 so that the pump work space 22 is connected with the pumpinterior 12. During the discharge stroke of the stroke of the pumppiston 26, the fuel now flows out of the pump work space 32 via thefilling groove 35 into the pump interior 12, so that no pressureexceeding the opening pressure of the injection nozzle 37 can be builtup in the pump work space 32. Accordingly, no fuel is fed to theinjection nozzle 37, and the internal combustion engine stops because ofthe lack of fuel. In the axial displacement position of the pump piston21, the bore 61 is open in the direction of the control space 44, sothat the fuel still being fed by the feeding pump 18, can flow into thepump interior 12 via the bore 61 when the second control valve 55 isclosed.

The second embodiment of a distributor fuel injection radial pistonpump, which is shown in FIG. 2, differs from the fuel injection pump inFIG. 1 only in that the annular groove 33 on the distributor piston 21,which annular groove 33 defines the pump work space 32, is divided by aring land 62 having an external diameter corresponding to the externaldiameter of the distributor piston 21. The ring land 62 is locatedwithin the annular groove 33 in such a way that the ring land 62,together with the inner wall of the distributor cylinder 22, separatesthe left-hand portion of the annular groove 33 in FIG. 2 from theright-hand portion of the annular groove 33 and, accordingly, from thepump work space 32, in the axial displacement position, shown in FIG.2b, occupied by the distributor piston 21 during a defect in the firstcontrol valve 43. Since the filling groove 35 opens into this portion ofthe annular groove 33 which is now sealed off, the filling groove 35 isseparated from the pump work space 32 in the axial displacement positionof the distributor piston 21 in each of its rotational positions and,accordingly, blocks the pump work space 32 relative to the pump interior12 which is filled with fuel. Accordingly, during the suction stroke ofthe pump piston 26 no fuel can reach the pump work space 32, and thedelivery of fuel from the pump work space 32 to the injection nozzle 37is prevented. In contrast to the fuel injection pump in FIG. 1, theaxial length of the filling groove 35 in this instance is dimensioned soas to be shorter, and the filling bore 38 is located at a greaterdistance from the end of the distributor cylinder 22 on the pumpinterior side, so that the filling groove 35 is not opened to the pumpinterior 12 by the distributor cylinder 22 in the axial displacementposition of the distributor piston (FIG. 2b).

Instead of providing a ring land 62, the annular groove 33 itself can beformed so as to be narrow enough that it is overlapped by the throughholes 25 in the distributor cylinder 22 in the normal operating positionof the distributor piston 21 (FIG. 2a), and is covered by the inner wallof the distributor cylinder 22 in the axial displacement position of thedistributor piston 21 (FIG. 2b) in its full length.

Another embodiment of a distributor fuel injection radial piston pumptype shown in FIG. 3 differs from the fuel injection pump in FIG. 1 inthat a by-pass 63 is provided in the relief line 50, which by-pass 63bridges the first control valve and is opened or closed by thedistributor piston 21. For this purpose, a first by-pass portion 64 isconnected with the first bore portion 51 of the relief line 50 and asecond by-pass portion 65 is connected with the second bore portion 52of the relief line 50. Every by-pass portion 64, 65 opens into theinterior of the distributor cylinder 22. The openings are arranged insuch a way that they are sealed off by the distributor piston 21 in thenormal operating position of the distributor piston 21 (FIG. 3a) andopen into the control space 44 in the axial displacement position (FIG.3b) occupied by the distributor piston 21 during a defect in the firstcontrol valve 43. The pump work space 32 is accordingly connected withthe pump interior 32 in the axial displacement position of thedistributor piston 21 in all of its rotational positions via the controlspace 44, which closes the by-pass 63, and the relief line 50 so thatthe fuel which is located in the pump work space 32 is supplied to thepump interior 12 during the discharge stroke of the pump piston 26 viathe relief line 50. Also, in this instance, fuel feeding to theinjection nozzle 37 is prevented in the axial displacement position ofthe distributor piston 21 which resulted from the closing of the secondcontrol valve 55.

The embodiment of a distributor fuel injection radial piston shown inFIG. 4 is somewhat more extensively modified relative to the fuelinjection pump in FIG. 1 than the embodiment examples in FIGS. 2 and 3.The pressure line 20 leading from the delivery pump 18 is directlyconnected with the pump interior 12. The control space 44 in thedistributor cylinder 22 is connected with the pump interior 12 via aninflow line 66 and is connected to an outlet opening 69 provided in thecover 11 via an outflow line 7 with the intermediary of a throttle 68.The outlet opening 69 communicates in turn with the fuel tank via a fuelreturn line. The second control valve 55 is arranged in the inflow line66. The connection of the drive shaft 15 and the distributor piston 21is effected in such a way that the front side 70 of the distributorpiston 21 projecting into the pump interior 12, is acted upon by thefuel pressure prevailing in the pump interior 12.

If the first control valve 43 remains stuck in its closing position dueto a defect, the second control valve 55 is controlled--as in the fuelinjection pump in FIG. 1--the monitoring device 60. This second controlvalve 55 closes, so that no more fuel can flow out of the pump interior12 into the control space 44 via the inflow line 66. Only the connectionof the control space 44 to the outlet opening 69 via the outflow line 67remains intact. There is now n counter-pressure in the control space 44opposed to the pressure acting on the front side 70 of the distributorpiston 21, so that the distributor piston 21 is displaced to the rightin FIG. 4a and occupies its axial displacement position shown in FIG.4b. In this displacement position, the filling groove 35 is displacedfar enough to the right that it is no longer capable of overlapping thefilling bore 38 in the distributor cylinder 22 (FIG. 4b). The pump workspace 32 is accordingly separated from the pump interior 12 and can nolonger be filled with fuel during the suction stroke of the pump piston26. During a defect in the first control valve 43 the fuel feeding tothe injection nozzle 37 is interrupted.

The embodiments of the distributor fuel injection pumps according toFIGS. 2-4 differs from the fuel injection pump in FIG. 1 only by themodifications mentioned above. Moreover, the construction and manner offunctioning are the same, so that the same reference numbers have alsobeen used for the same structural elements. For the sake of simplicity,the reference numbers in FIGS. 2-4 are only entered as required forunderstanding the differences relative to FIG. 1.

What is claimed:
 1. A distributor fuel injection radial piston pump forfeeding fuel to at least one injection nozzle of an internal combustionengine, said pump comprising:a housing defining a pump interior; atleast one pump piston located in said housing and defining at leastpartially a pump working space, said one pump piston being displaceablein said housing to perform a suction stroke during which said pumpworking space is filled with fuel, and a discharge stroke during whichfuel is fed from said pump working space to the one injection nozzle; adistributor piston having an end face and being axially displaceablebetween a first axial position in which it enables communication of saidpump working space with the injection nozzle and a second axial positionin which it prevents communication of said pump working space with theinjection nozzle; a first control valve for controlling a quantity offuel fed to the injection nozzle, said first control valve being movablebetween open and closed positions to communicate said pump working spacewith said pump interior therethrough in the open position thereof toprevent feeding of fuel to the injection nozzle and blockingcommunication between said pump working space and said pump interiortherethrough in the closing position thereof to provide for feeding fuelto the injection nozzle; and means for preventing excessive feeding offuel to the nozzle in case of failure of said first control valve tomove from the closed position thereof to the open position thereof inresponse to a predetermined control signal, said prevent means includinga control space defined at least partially by said end face of saiddistributor piston and a second control valve for changing pressure insaid control space to move said distributor piston to the second axialposition thereof in which feeding of fuel to the injection nozzle isprevented.
 2. A pump according to claim 1 further comprising:drive meansfor displacing said pump piston and including a drive shaft and camdrive means connected to said drive shaft for reciprocally displacingsaid pump piston radially relative to said drive shaft to cause saidpump piston to perform the suction and discharge strokes; and adistributor cylinder arranged coaxially with said drive shaft and havinga plurality of bores; said distributor piston being received in saiddistributor cylinder and having an end opposite to said end face andprojecting from said distributor cylinder, said distributor pistonhaving a circumference and a plurality of grooves formed on saidcircumference, and said distributor piston being connected with saiddrive shaft at said opposite end thereof for axial displacement relativethereto between said first and second axial positions and for jointrotation therewith between first and second rotational positions, saidplurality of grooves of said distributor piston cooperating with saidplurality of bores of said distributor cylinder to connect said workingspace with said pump interior in the first axial position and in thefirst rotational position of said distributor piston and to connect saidpump working space with the injection nozzle in the first axial positionand the second rotational position of said distributor piston, and toeffect one of connecting said pump working space with said interior inthe second axial position and in the second rotational position of saiddistribution piston and blocking connection between said pump workingspace and said pump interior in the second axial position and the firstrotational position of said distribution piston.
 3. A pump according toclaim 2 comprising a feeding pump for feeding fuel into said pumpinterior and a pressure line for communicating fuel from said feedingpump to said pump interior.
 4. A pump according to claim 3 furthercomprising means for increasing pressure in said control space.
 5. Apump according to claim 3 further comprising means for decreasingpressure in said control space.
 6. A pump according to claim 3, whereinsaid pressure line extends through said control space and has a lineportion extending between said control space and said pump interior andincluding an outlet opening and a throttle therein, said second controlvalve being arranged in said line portion.
 7. A pump according to claim6 further comprising a bore communicating said distributor cylinder withsaid pump interior, said bore being overlapped by said distributorpiston and communicating with said control space only in the secondaxial position of said distributor piston.
 8. A pump according to claim6, wherein said plurality of grooves of said distributor pistoncomprises an annular groove defining together with said pump piston saidpump working space and an axial filling groove, said plurality of boresof said distributor cylinder including a filling bore communicating saidannular groove of said distributor piston with said pump interior viasaid filling groove in the first rotational position of said distributorpiston, and said filling groove having a length dimensioned in such away that it projects out of said distributor cylinder into said pumpinterior in the second axial position of said distributor piston.
 9. Apump according to claim 6, wherein said plurality of grooves includes anannular groove defining together with said pump piston said pump workingspace, and an axial filling groove, said distributor piston having aring land having an external diameter equal to that of said distributorpiston and dividing said annular groove in a first portion communicatingwith said filling groove and a second portion, said distributor cylinderhaving an inner wall cooperating with said ring land to blockcommunication between said first and second portions of said annulargroove in the second axial position of said distributor piston, saidplurality of bores of said distributor cylinder including a filling borecommunicating with said first portion of said annular groove via saidfilling groove.
 10. A pump according to claim 6, wherein said pluralityof grooves of said distributor piston comprises an annular groove havingan axial length defining together with said pump piston said pumpworking space and an axial filling groove, said plurality of bores ofsaid distributor cylinder including a filling bore communicating saidannular groove with said pump interior in the first position of saiddistributor piston, said distributor cylinder having an inner walloverlapping completely the axial length of said annular groove in thesecond axial position of said distributor cylinder.
 11. A pump accordingto claim 6, further comprising a by-pass having first and second by-passportions, a relief line having a first relief line portion extendingbetween said first control valve and said pump working space and asecond relief line portion extending between said first control valveand said pump interior, said first by-pass portion communicating withsaid first relief line portion and said second by-pass portioncommunicating with said second relief line portion, said by-pass beingblocked in the first axial position of the distributor piston andcommunicating with said control space in the second axial position ofthe distributor piston.
 12. A pump according to claim 1, furthercomprising an inflow line communicating said control space with saidpump interior, an outlet opening in said pump interior, and an outflowline for communicating said control space with said outlet opening, saidoutlet opening having a throttle said second control valve beingarranged in said inflow line, and said opposite end of said distributorpiston having an end surface acted upon by the pressure in said pumpinterior.
 13. A pump according to claim 12, wherein said plurality ofgrooves of said distributor piston includes an annular groove definingtogether with said pump piston said pump working space and an axialfilling groove, said plurality of bores of said distributor cylinderincluding a filling bore communicating in the first rotational positionof said distributor piston said annular groove via said filling groovewith said pump interior, said filling groove having an axial lengthdimensioned in such a way that it clears said filling bore in the secondaxial position of said distributor piston.
 14. A pump according to claim1 further comprising a device for monitoring functioning of the firstcontrol valve and for communicating a closing command to said secondcontrol valve when said first control valve fails to move from theclosing position in response to the predetermined control signal.
 15. Apump according to claim 14, wherein said monitoring device comprises aspeed detector for generating the closing command in response to anengine speed exceeding a predetermined maximum speed.
 16. A pumpaccording to claim 14, wherein said second control valve is an electriccontrol valve formed in such a way that it is closed in its unexcitednormal position and is opened in its excited work position.
 17. A pumpaccording to claim 1, wherein said first control valve is an electriccontrol valve.